Electronic supplementary material

A workflow for the rapid assessment of the landslide-tsunami hazard in perialpine lakes

Michael Strupler, Flavio S. Anselmetti, Michael Hilbe, Katrina Kremer, and Stefan Wiemer

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1. Forecasted peak ground accelerations for Switzerland

Fig. ESM.1. Interpolated median PGAs expected for mean return periods of 475 (top) and 2475 years (bottom) in Switzerland. PGA values are in m/s2. Coordinate Reference System: CH1903+. Data from Wiemer et al. (2016)

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2. Sedimentation model

푇푃푀푆(i,j) is calculated as function of its water depth and slope gradient with the following linear regression (Equation ESM.1; Strupler et al. 2018):

푢푛푖푡=푆푀푈4

푇푃푀푆(푖, 푗) = ∑ 푢 푛푖푡 푎푔푒 푖푛푡푒푟푣푎푙 [푦푟] × 0.01 × (푎(푖, 푗)) + 푏 × 푤푑(푖, 푗) − 푐 푢푛푖푡=푆푀푈3 × 훼(푖, 푗) (1)

For the Holocene drape in Lake , two different units (termed “SMU3” and “SMU4” in Strupler et al. (2018b)) with different sedimentation rates can be identified: a stratigraphically lower/older lying Holocene sedimentary unit that spans ~ 5000 years and an upper/younger Holocene unit that spans ~7000 years (Strasser 2008; Strupler et al. 2018). The potentially mobile sediment results from the summation of the two unit thicknesses at each pixel (i,j). Used coefficients are shown in Table ESM.1.

Table ESM.1. Coefficients used in Equation ESM.1

Unit Age interval (years) a b c SMU3 5000 0.047 0.000175 0.001305 SMU4 7000 0.021 0.000104 0.000654

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3. Lake

Comparison of TPMS (this study) to measured Holocene thickness (Strasser et al. 2007) Holocene sedimentation rates (i.e. < 11500 cal yr B.P.) at three slope locations in are ~22 cm/ka (Weggis site), ~36 cm/ka (St.Niklausen site), and ~42 cm/ka (Chrütztrichter site), which would correspond to a drape thickness of ~2.5, ~4., and ~4.8 m at their investigated sites (Strasser et al. 2007). In comparison, the potentially mobile sediment modelled with the approach of Strupler et al. (2018b) does not show a systematic over- or underestimation. However, there are differences between ~20 and ~50 %.

Table ESM.2. Location, measured and modelled Holocene drape of long cores from Strasser et al. (2007) that show an undisturbed Holocene sediment drape. Water depth (WD) and slope were sampled from the bathymetry based on the core location. Core coordinates from Strasser (2008) with Coordinate

Reference System CH1903 were converted to CH 1903+. TStrasser2007 = measured thickness by Strasser et al. (2007), TPMS = Thickness of the potentially mobile sediment calculated in this study.

Core Name X Y WD Slope TStrasser2007 TPMS Diff. [%] 4WS05-K1 2668474 1208744 35.2 6.1 2.5 3.7 48 4WS05-K4 2672225 1209150 57.2 14.6 4.1 3.1 -24 4WS05-K6 2675025 1208983 32.2 5.2 4.8 3.8 -21

Fig. ESM.2. Comparison of TPMS to measured Holocene thickness from Strasser et al. (2007)

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Plots of landslide volumes

Fig. ESM.3. Potential landslides in Lake Lucerne for a mean RP of 475 (a) and 2475 years (b)

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4. Lake

Bathymetry

Fig. ESM.4. Bathymetry of Lake Zug

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Landslide characteristics

Fig. ESM.5. Characteristics of potential landslides forecasted for Lake Zug for RP=475 (red) and 2475 years (cyan).

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Location of forecasted landslides and 훈ퟎퟐ퐃

Fig. ESM.6. Location of forecasted landslides and characteristic tsunami amplitudes in Lake Zug for PGAs with RP=475 (a) and 2475 years (b) 8

5. Lake

Bathymetry

Fig. ESM.7. Bathymetry of Lake Walensee

Landslide characteristics

Fig. ESM.8. Characteristics of potential landslides forecasted for Lake Walensee for RP=475 (red) and 2475 years (cyan).

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Location of forecasted landslides and 훈ퟎퟐ퐃

Fig. ESM.9. Location of forecasted landslides and characteristic tsunami amplitudes in Lake Walensee for PGAs with RP=475 (a) and 2475 years (b).

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6. List of used R Libraries

Table ESM.3. R libraries used in the workflow

Library Reference cowplot Wilke 2019 ggpubr Kassambara 2019 ggrepel Slowikowski 2019 ggsn Santos Baquero 2019 knitr Xie 2019 lwgeom Pebesma 2019b pracma Borchers 2019 raster Hijmans 2019 RColorBrewer Neuwirth 2014 rgdal Bivand et al. 2019 rgeos Bivand and Rundel 2019 rmapshaper Teucher and Russell 2018 RPyGeo Brenning et al. 2018 scales Wickham 2018 sf Pebesma 2019a Smoothr Strimas-Mackey 2018 stringr Wickham 2019 tidyverse Wickham 2017 units Pebesma et al. 2019

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7. References

Bivand R, Keitt T, Rowlingson B (2019) Rgdal: Bindings for the ’geospatial’ data abstraction library

Bivand R, Rundel C (2019) Rgeos: Interface to geometry engine - open source (’geos’)

Borchers HW (2019) Pracma: Practical numerical math functions

Brenning A, Polakowski F, Becker M (2018) RPyGeo: ArcGIS geoprocessing via python

Hijmans RJ (2019) Raster: Geographic data analysis and modeling

Kassambara A (2019) Ggpubr: ’Ggplot2’ based publication ready plots

Neuwirth E (2014) RColorBrewer: ColorBrewer palettes

Pebesma E (2019a) Sf: Simple features for r

Pebesma E (2019b) Lwgeom: Bindings to selected ’liblwgeom’ functions for simple features

Pebesma E, Mailund T, Kalinowski T (2019) Units: Measurement units for r vectors

Santos Baquero O (2019) Ggsn: North symbols and scale bars for maps created with ’ggplot2’ or ’ggmap’

Slowikowski K (2019) Ggrepel: Automatically position non-overlapping text labels with ’ggplot2’

Strasser M (2008) Quantifying Late Quaternary Natural Hazards in Swiss Lakes - Subaquatic Landslides, Slope Stability Assessments , Paleoseismic Reconstructions and Lake Outbursts. ETH Zurich; Schweizerische Geotechnische Kommision, Dissertation ETH Zurich

Strasser M, Stegmann S, Bussmann F et al (2007) Quantifying subaqueous slope stability during seismic shaking: Lake Lucerne as model for ocean margins. Marine Geology 240:77–97. doi: 10.1016/j.margeo.2007.02.016

Strimas-Mackey M (2018) Smoothr: Smooth and tidy spatial features

Strupler M, Danciu L, Hilbe M et al (2018) A subaqueous hazard map for earthquake-triggered landslides in Lake Zurich, Switzerland. Natural Hazards 90:51–78. doi: 10.1007/s11069-017-3032-y

Teucher A, Russell K (2018) Rmapshaper: Client for ’mapshaper’ for ’geospatial’ operations

Wickham H (2017) Tidyverse: Easily install and load the ’tidyverse’

Wickham H (2019) Stringr: Simple, consistent wrappers for common string operations

Wickham H (2018) Scales: Scale functions for visualization

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Wiemer S, Danciu L, Edwards B et al (2016) Seismic Hazard Model 2015 for Switzerland. Swiss Seismological Service (SED) at ETH Zurich. 1–163. doi: 10.12686/a2

Wilke CO (2019) Cowplot: Streamlined plot theme and plot annotations for ’ggplot2’

Xie Y (2019) Knitr: A general-purpose package for dynamic report generation in r

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